Polymer blend compositions containing starches or starch derivatives are well known. Such compositions are generally desired to be biodegradable, as well as to possess a wide variety of other physical, thermal, and/or chemical properties. Exemplary publications disclosing polymer compositions comprising starches or starch derivatives include the following.
U.S. Pat. No. 4,337,181 describes biodegradable film-forming formulations comprising starch, ethylene-acrylic acid copolymer, and optionally polyethylene for use in agricultural mulch, garbage bags, and various types of packaging. According to the disclosure, the ethylene-acrylic acid copolymer must be neutralized and the moisture content in the formulation must be adjusted before a suitable film can be fabricated.
U.S. Pat. No. 5,095,054 describes thermoplastic polymer blend compositions containing destructurized starch and either a substantially water-insoluble thermoplastic polymer or another polymer component or both. According to the disclosure, the other polymer component is at least one of: 1) a polymer containing at least two different types of functional groups, one being hydroxyls; 2) a polymer not containing hydroxyl groups but containing at least two other different types of functional groups, one being carboxylates; 3) a polymer containing tertiary amino or quaternary ammonium groups; 4) a polysaccharide chemically modified to contain hydroxyalkyl, alkyl ether, and/or ester groups; 5) a vinyl pyrrolidone copolymer; 6) a cationically-modified polysaccharide; 7) an anionically-modified polysaccharide; 8) a vinyl alcohol-olefin copolymer, made by hydrolyzing a vinyl ester-olefin copolymer; 9) a polysaccharide graft copolymer or derivative thereof; 10) a polyalkyleneimine polymer or copolymer; 11) a styrene-sulfonic acid polymer or copolymer, or a salt thereof; and 12) a polymer or copolymer containing partially or fully neutralized carboxylic acid groups and no other functional groups.
U.S. Pat. No. 5,234,978 describes a biodegradable composition comprising an unsaturated hydrocarbon polymer, a lower alkyl or hydroxyalkyl ether of starch having a degree of substitution of at least 0.25, a polyhydric alcohol having 2–10 carbon atoms and 2–6 hydroxyl groups, and a compatibilizing agent. According to the disclosure, the compatibilizing agent can be a vinyl copolymer, acrylic copolymer, or a mixture thereof.
U.S. Pat. No. 5,262,458 describes biodegradable articles and methods for forming such articles. According to the disclosure, the articles comprise destructurized starch, an ethylene-acrylic acid copolymer, and a product of the interaction of ethylene-acrylic acid copolymer and starch particles smaller than 1 micron. Optionally, urea and/or ammonia may also be added to the articles. The method of obtaining such biodegradable articles is also set forth to comprise the steps of extruding the starch, ethylene-acrylic acid copolymer, and optionally water, urea, and/or ammonia, from 90° C. to 150° C., reducing the water content to below 6% by weight, and injection molding or extrusion blowing the resulting composition.
U.S. Pat. No. 5,288,765 and International Publication No. WO 91/02023 both describe expanded articles, and methods of making such articles using extrusion, each comprising a composition including starch, a polymer compatible with starch (i.e., ethylene-acrylic acid and/or ethylene-vinyl alcohol copolymer(s)), and an expanding agent. According to the disclosure, the expanding agent is preferably sodium bicarbonate. U.S. Pat. No. 5,360,830 describes similar expanded articles that are further characterized by a closed pore structure and a density of from 0.01 to less than 0.1 g/cm3.
U.S. Pat. No. 5,292,782 describes a biodegradable polymeric composition that contains starch, a synthetic thermoplastic polymer, and a plasticizer that is a polyol or a derivative, reaction product, or oxidation product thereof. According to the disclosure, the starch and the synthetic thermoplastic polymer form a structure in which they are at least partially interpenetrated at the molecular level.
U.S. Pat. Nos. 5,334,634 and 5,462,982, as well as European Patent No. EP 0 758 669 A2, describe biodegradable polymer compositions, articles made therefrom, and processes for preparing such compositions. In each case, the composition is disclosed to comprise a destructured starch (or a starch in combination with a destructuring agent such as urea), a thermoplastic polymer such as an ethylene-vinyl alcohol copolymer, and a high-boiling plasticizer such as glycerol. According to the disclosures, no water is added to assist in destructuring the starch.
U.S. Pat. No. 5,412,005 describes biodegradable polymeric compositions that contain a starch-based component and a polymeric component, which itself contains polymers of hydroxyacids or mixtures thereof with polymers deriving from ethylenically unsaturated monomers, e.g., such as PVA and EVA.
U.S. Pat. No. 5,449,708 describes a starch-based biodegradable polymer, as well as a method for its continuous preparation. According to the disclosure, the starch-based biodegradable polymer is taught to be a homogeneous mixture of starch, an ethylene-acrylic acid copolymer, a salt of stearic acid, and an aqueous lubricant material.
U.S. Pat. No. 5,569,969 describes a starch-based composition and a method for producing biodegradable articles therefrom. The starch-based composition contains a starch, a destructuring agent, a plasticizer, and optionally polyvinyl alcohol and/or ethylene-vinyl alcohol. According to the disclosure, the destructuring of the starch takes place between 120° C. and 170° C., while below the plasticizer boiling point. The composition without PVA and/or EVA is disclosed to be suitable for extrusion, while that with the optional component(s) is disclosed to be suitable for blow molding, injection molding, or thermoforming.
U.S. Pat. Nos. 5,801,207 and 5,589,518 relate to biodegradable foamed articles and processes for preparation of such articles, respectively, such that the foamed articles have a density of 5–300 kg/m3 and are formed from agglomerated particles comprising 30–98.5% by weight of a thermoplastic natural polymer capable of absorbing at least 15% of its weight of water (e.g., a thermoplastic starch), 1.5–70% by weight of a thermoplastic polymer, and 0–20% by weight of water. According to the disclosures, a bonding agent is also present to allow compressive bonding of the particles into a closed cell foam.
U.S. Pat. No. 5,654,353 describes a degradable starch resin composition, as well as a process for preparation and a use of such a composition. According to the disclosure, the composition is a starch concentrate made by mixing starch, a mixing promoter, a plasticizer, a biodegradation accelerator containing a bioactive agent, and an alkaline additive. Also according to the disclosure, the process for preparation comprises selecting the biodegradation accelerator, preparing the modified starch concentrate, and extruding and pelletizing a mixture of the modified starch concentrate, an ethylene-acrylic acid copolymer, and a polyvinyl resin. The product is disclosed to be particularly useful for light or heavy packaging films or for agricultural films.
U.S. Pat. No. 5,741,521 describes a biodegradable or digestible matrix and its use in the controlled release of an agriculturally active agent. The biodegradable or digestible matrix contains an amylaceous material, optionally in association with a synthetic polymer. According to the disclosure, the amylaceous material is not destructured and includes amylose or a starch, along with an optional filler.
U.S. Pat. No. 5,587,486 describes a biodegradable composition containing a matrix, which includes a starch component, at least one synthetic thermoplastic polymeric component, and a fluidizing agent, with a natural organic filler material dispersed in the matrix. According to the disclosure, the fluidizing agent can be a fatty acid, a fatty alcohol, a polyether or polyglycol ether, an ester or amide of a fatty acid, a reaction product of a fatty acid with a polyglycerol, or a mixture thereof.
U.S. Pat. No. 6,096,809 describes a biologically degradable polymer mixture containing at least one starch biopolymer made from renewable raw materials, a plasticizer, and one or more of the following polymers: aromatic polyester, aliphatic-aromatic polyester block copolymer, polyesteramide, polyglycol, and polyester urethane.
European Patent No. EP 0 942 040 A1 describes a polymeric film comprising 10–60% of starch, 5–20% of a coupling agent such as an ethylene-acrylic acid or ethylene-vinyl acetate copolymer, 20–90% of a stabilizing agent such as polyethylene, 20–60% w/w of starch and water or gelatinizing and plasticizing agents such as urea or carbamide, and 2–10 parts per hundred resin of oligosaccharides. Additionally, this disclosure includes a process taught to be useful for preparing such a polymeric film.
It is desirable to identify compositions containing starch that have advantageous combinations of properties so that any articles made from them have, for example, good degradability, sufficient mechanical properties such as resiliency and tensile or compressive strength, and ease of processability, just to name a few. The present invention identifies such compositions, methods of making them, and articles containing them or formed by the methods of the invention.